Guys and girls opinions? Is my boyfriend too amazing or am I just really insecure?

My boyfriend and I have been dating a year and a half. We used to check out other people, and it was no big deal. Then one time my boyfriend came out and said it bothered him when I checked out other guys because he felt he wasn't important enough. I didn't understand what the problem was and he said he didn't check out other girls anymore because he wanted to be as close to me as possible without feeling like there was another guy better than him. So needless to say, he gave me a taste of my own medicine to see how I liked it and it opened my eyes to how he felt and now I don't even have the desire to check out other guys because I love him so much and honestly, he is the only attractive one I see. However, lately I've been thinking what if he's lying? He's given me no reason to think he is, and he always promises he doesn't check out other girls cuz he has no desire. He knows how much promises mean to me so I don't think he would promise something he didn't mean. I recently asked two of his friends if he checked out other girls. One just said he didn't and the only girl he talks about is me. And the other friend said whenever he would say something about a girl, my boyfriend would say "man I got myself a girl and she's wonderful, I'm not about to mess that up". So if he can be a man and say that to a good friend, then why would I think he's lying? Is he too good to be true? Am I just super insecure? And after all the talks and promises we made about not checking out others, idk why I would even question it. Is there any guy out there like my bf who doesn't check out other girls? Need opinions!